Undesired heat loss from production tubing as well as uncontrolled heat transfer to outer annuli can be detrimental to the mechanical integrity of outer annuli, because productivity losses from the well due to deposition of paraffin and asphaltene materials, accelerate the formation of gas hydrates, and destabilize the permafrost in arctic type regions. The successful use of wellbore insulation fluids in the past several years has demonstrated that such fluids, added either into annulus or riser, can effectively reduce undesired heat loss.
For instance, U.S. Pat. No. 6,489,270 discloses non-crosslinked insulating fluids which are easy to blend and pump into the annulus. Such fluids, when added either into an annulus or riser, effectively reduce undesired heat loss from the production tubing, or heat transfer to outer annuli.
Water-superabsorbent polymers are disclosed for use in gelled fluids as thermal insulating fluids in U.S. Patent Publication No. 20040059054. Such gelled fluids exhibited an inherently low thermal conductivity and the requisite viscosity. The fluid viscosity was generated by mixing the requisite amount, typically between from 0.1 to 10 weight percent, of polysaccharide into a brine system which may optionally contain a glycol, such as propylene glycol and a viscosifying polymer, such as carboxymethyl hydroxypropyl guar. The resulting fluid, which are easy to blend and pump at the rig site, reduces the heat loss from a hot annulus to a cold annulus by reducing the fluid thermal convection caused by the temperature differential between the high temperature environment of the inner annulus and low temperature environment of the outer annuli. Fluid thermal convection, which accounts for the major portion of the heat transfer, is dependent on the fluid viscosity and mobility of the solvent, such as a water-polyol mixture.
Alternative materials which are more effective in the retention of heat have been sought. Such materials are needed in order to improve the intrinsic thermal conductivity of the solvent system of insulation fluids.